Glass - Back to the Future!

Presenting Author:
Jens Bliedtner

article posted 21 March 2016

Jens Bliedtner studied precision engineering at the Friedrich-Schiller-University in Jena. He wrote his doctoral thesis in the fields of development of pulsed laser systems and special methods in macro material processing. Since 2000 Bliedtner has been a professor at the Ernst Abbe University of Applied Sciences in Jena and the head of the team production engineering and automation of production processes. Currently he is working in the research fields of optical technology and laser material processing.

Development of a reflector system to enhance efficiency and quality of the laser-based glass tube joining process

Daniel Eilenberger, Thomas Schmidt & Jens Bliedtner>
ifw - Günter-Köhler-Institut für Fügetechnik und Werkstoffprüfung GmbH, Otto-Schott- Str.13, D-07745 Jena, Germany

The joining of glass tubes is an established and common procedure which is applied especially in the fields of pharmaceutics, chemistry, lighting and environmental engineering and solarthermics. The most frequently used technology in this process is based on a gas torch as heat source. Such a torch is a low-cost tool on the one hand, but has an unfavourable balance of energy on the other hand. In contrast to that, the joining process based on a CO2-laser is a relatively new procedure, which is getting more and more accepted due to its manifold advantages such as e.g. a lower energy demand, a shorter process time, no chemical influence of the flame, no pollution through combustion residues, and a higher degree of automation. However, there are still considerable losses in this process through heat emission and reflected laser radiation, which prevent a better energy efficiency and thus a faster introduction to the market.

Picture 1: interaction between CO2-laser radiation and glass A mirror system shaped like a closed reflecting wall was developed at ifw in order to use these kinds of radiation. Thus, the new system enables the feedback of the heat and laser radiation into the joining zone on the one hand and on the other hand it prevents the convection on the glass surface. Compared to conventional laser-based glass tube joining process ~25% laser power could be saved. Furthermore, the additional radiation input has positive effects on the development of tensions after the joining process so that a time- consuming temper process could be avoided.

The poster shows a comparison of the two laser-based glass tube joining processes with and without mirror system on borosilicate glass tubes having a diameter of 100mm. The most important differences as well as the similarities are shown in terms of energy distribution, temperature gradient, process time, quality of the joining zone, and induced thermal stress. The positive influence of the mirror system on the high temperature gradient, which was created by laser radiation, is also shown. Finally, there is an illustration of the setup and the function of the mirror system.